The conventional structure of a powder press is the arrangement of a die (press die) on a die plate which rests on a machine frame. At least one upper punch and one lower punch cooperate with the die and which are preferably driven by a hydraulic drive. It is known to attach the punch to a so-called adaptor plate which is vertically guided in appropriate guide columns or the like. The punches are directly attached to the adaptor plate or via an adaptor which, in turn, is fastened to the adaptor plate.
It is further known to carry out the compression of the powder in the die according to force and distance parameters. Therefore, force measuring devices are associated with the punches. The distance measurements are carried out by corresponding distance measuring systems. Generally pressure cells are associated with the force measurement.
Naturally, the dimensions of the punches and the die are known and/or may be identified. In order to be able to carry out a very accurate measurement of the distances, a reference is nevertheless required, as the identification of the dimensions, for example of the upper punch, does not indicate anything about its precise height in the press zone, namely in the upper end position. In the prior art, the referencing process is generally carried out by a setter, by means of, for example, an end measure and a straight edge and is subject to variations for each referencing process of one to two hundredths of a millimetre. In this connection, defined positions of the punches are referenced to a defined position of the die. All movements of the punches relate to this reference. When changing the tools, the punches have to be referenced again each time, as the dimensions of the punches and die change. In some situations, a plurality of upper and lower punches and, for example, a centre pin are used which respectively have to be referenced. Such a referencing process is, therefore, time-consuming and does not guarantee the desired consistency. If it is desired to change the forming tools automatically, it is not possible to carry out manual referencing.
The object of the invention is to provide a method for determining a reference for a powder press, which may be automatically carried out and which allows the tools to be automatically changed with, at the same time, sufficiently accurate consistency of the identified reference values.